Hi Mariog,

Thanks for your reply.

Your speculation is quite logical.

Just follow the clue your provided. I get the defination "h_D".

h_D is the radial distance from bolt circle to circle on which HD acts;(EN 13445-3 Annex D)(and I hope it is right, hah)

Regarding the "m", I think it is gasket factor, as it is used to calcualte the pressure P_max.

By the way, do you have any clue for η_SR(I)in (G.23) of EN 1591?

thanks.